Typically, commercial lawnmowers are capable of traveling over the ground at relatively high speeds of between five and six miles per hour, are relatively stable on slopes and unpaved surfaces, and are able to move up close to objects such as trees and shrubs with sufficient control to avoid damaging the plants, and are able to extend the mower deck under fences and shrubs where ground clearances are restricted. Usually the operator will be seated or standing near the turning center of the mower so as to minimize the centrifugal force he experiences in a tight turn, which not only reduces his ability to control the mower, but also adds to his fatigue during long periods of operation.
A mower of this type is disclosed in U.S. Pat. No. 5,507,138, issued Apr. 16, 1996, entitled "Power Mower with Riding Platform for Supporting Standing Operator."
High maneuverability is an essential characteristic of commercial landscaping mowers of this type. It is achieved by combining the propulsion and turning functions in driving the wheels. That is, on each side of the machine, independent drive wheels are powered by the engine in either forward or reverse directions. The wheels cannot steer in a conventional manner. Caster wheels are mounted in front of the mower deck allowing the machine to swivel around, turning on an axis between the rear drive wheels. The operator stands or sits at the turning axis to minimize the turning forces on him in tight turns.
A major problem with such mowers is the degree of training and skill required of the operator to efficiently operate the machine. Typically, a pair of hand levers, one on each side of the operator's station, control independent hydrostatic drives powered by the engine. The technique of driving by levers that are pushed or pulled to independently vary the speed and direction of the drive wheels. Is an acquired skill not well within the training and skill of the ordinary person familiar with driving an automobile, where the propulsion and steering are separate functions, and unlikely to be familiar with a system combining the propulsion and steering into one function using separate hand levers.
In addition, such mowers are expensive to maintain. The independent hydrostatic drive systems essentially have duplicate components and controls of non-automotive specifications. When something goes wrong with one of the dual systems, the machine cannot be operated successfully or fixed by automotive type mechanics.
Also, the caster wheels are set out ahead of the mower deck and on spindles that extend above the mower deck limiting the accessibility of the mower under low objects, such as fences, or traveling up close to buildings and trees.